class Tixing { 
   double above,bottom,height;
   Tixing(double a,double b,double h) {
      above = a;
      bottom = b;
      height = h; 
   }
   double getArea() {
      return (above+bottom)*height/2;
   }
}
class Student {
   double computerArea(Circle c) {
      double area=c.getArea();
      return area;
   }
   double computerArea(Tixing t) {
      double area=t.getArea();
      return area;
   }
}
class Circle {
    double radius,area;
    void setRadius(double r) {
        radius=r;
    }
    double getArea(){
        area=3.14*radius*radius;
        return area;
    }
}public class Example4_13 {
  public static void main(String args[]) {
      Circle circle = new Circle();
      circle.setRadius(196.87);
      Tixing lader = new Tixing(3,21,9);
      Student zhang = new Student();
      System.out.println("zhang计算圆的面积：");
      double result=zhang.computerArea(circle);
      System.out.println(result);
      System.out.println("zhang计算梯形的面积：");
      result=zhang.computerArea(lader);
      System.out.println(result);
   }
}
